The demand on engine lubricants has become more severe to cope with modern engine design with ever stronger anti-oxidation requirements. Thus, this forces additive companies to develop robust engine oils with stronger antioxidant and anti-nitration additives. Further to this is the firmly established issue of fuel economy which has become a very import issue for automotive manufacturers, lubricant additive companies, and automobile owners. Thus reducing friction between moving parts in the engine is paramount.
Primary antioxidants have long been part of lubricant additive formulations. They have been widely used to improve the thermal-oxidative stability and/or light induced oxidative degradation in numerous products used in engineering. For example, primary antioxidants can improve the performance properties in lubricants, hydraulic fluids, metal working fluids, fuels or polymers, just to name a few. Hindered phenolic anti-oxidants, a class of primary antioxidants, are capable of donating a hydrogen atom that reacts with alkyl radicals or peroxy radicals, thus interrupting the radical chain mechanism of the auto-oxidation process which results in the hindered phenol becoming a stable radical.
Furthermore, engine oil acts as a lubricant between moving engine parts at various conditions of load, speed and temperature. Hence, the various engine components experience different combinations of boundary layer, mixed, and (elasto) hydrodynamic regimes of lubrication. The largest frictional losses occur at piston liner/piston ring interfaces and a smaller part by the bearings and valve train. To reduce the energy losses due to friction of the various engine parts and to prevent engine wear, additives such as friction modifiers, anti-wear agents, and antioxidants are incorporated into the engine oil. Antioxidants tend to lengthen the effect of the afore-mentioned additives. Further, to reduce the hydrodynamic friction in the piston/cylinder, the viscosity of engine oils has been lowered. This has resulted in an increased the dependence on friction modifiers to offset the new boundary layer regime. Hence, a vast amount of effort has focused on the interaction of oil viscosity with various friction modifiers to improve fuel economy.
Although compounds combining boron with anti-oxidants are known in the art, as evidenced by EP 0089844, U.S. Pat. No. 3,347,793, U.S. Pat. No. 3,356,707, U.S. Pat. No. 3,359,298, U.S. Pat. No. 3,509,054, U.S. Pat. No. 4,474,670, U.S. Pat. No. 5,252,237, U.S. Pat. No. 5,698,499, U.S. Pat. No. 6,605,572, and U.S. Pat. No. 6,777,378; compounds with the outstanding oxidation and friction performance of those of the invention have not been described.
Thus, herein we report borated polyol hindered phenol antioxidant/friction modifier compounds and compositions containing same. These compounds and compositions enhanced performance in engine oils when compared with industry standard hindered phenolic antioxidants.